JP6842159B2 - Plasma processing method - Google Patents

Description

The present invention relates to a technique for performing plasma treatment on an object such as a substrate (particularly, an object in which copper is exposed on at least a part of the surface) to remove unnecessary organic substances from the surface, for example.

In the manufacturing process of a semiconductor substrate or the like, there are many situations where a process for removing unnecessary organic substances existing on the surface is required.

For example, in the process of manufacturing a semiconductor substrate, as shown in FIG. 1A, a photoresist layer 103 is placed on a substrate (for example, a semiconductor substrate made of silicon) 101 on which an electrode 102 is formed. Is formed, the mask pattern 104 is formed by exposing and developing the mask pattern 104, and the portion where the mask pattern 104 is not formed is etched to form a circuit pattern or the like. Here, in order to ensure the accuracy of etching, it is preferable that the mask pattern 104 formed on the substrate 101 has a straight shape in which the thickness does not change from the top surface portion to the root portion thereof. .. However, in reality, due to insufficient reaction of the photoresist or the like, as shown in the figure, a hemming portion 104a may be formed at the root of the mask pattern 104, or an eaves-shaped portion 104b may be formed on the top surface. Further, the development residue (so-called scum) 104c of the photoresist may remain in the gaps of the mask pattern 104 and the like, which may deteriorate the etching accuracy. Therefore, a process for removing these unnecessary portions 104a, 104b, 104c (so-called death come true process) is performed after the mask pattern 104 is formed and before the etching.

Further, for example, in the manufacturing process of a printed wiring board, as shown in FIG. 1 (b), on a substrate (generally composed of polyimide, epoxy resin, glass, silicon, etc.) 201 on which an electrode 202 is formed, A solder resist film (permanent protective film) 203 formed of a resin material or the like is formed, and a part thereof (a portion on which an electronic component is mounted) is irradiated with a laser or the like to form a via hole 204. If the solder resist residue (so-called smear) 204a generated when irradiated with this laser or the like remains inside the via hole 204 or the like, this may cause poor continuity or insufficient adhesion during interlayer connection. is there. Therefore, after the formation of the via hole 204, a treatment for removing the smear 204a (so-called desmear treatment) is performed.

Further, for example, in forming a comb-shaped electrode in a SAW (Surface Acoustic Wave) device, as shown in FIG. 1 (c), a substrate (for example, LiTaO ₃ (lithium tantalate) or LiNbO) is formed. _{By exposing and developing the photoresist layer formed on 3} (a substrate formed of a dielectric material such as lithium niobate) 301, a photoresist pattern 302 that covers a portion other than the comb-shaped pattern is formed. Then, a metal (for example, copper) to be an electrode is vapor-deposited on the metal to form the electrode layer 303. Then, the photoresist pattern 302 is removed together with the electrode layer 303 covering the photoresist pattern 302 to form a comb-shaped electrode 303. Here, if the photoresist residue 302a generated when the photoresist pattern 302 is removed adheres to the electrode 303 or the like, it may cause separation failure or the like. Therefore, after removing the photoresist pattern 302, a process for removing the development residue 302a of the photoresist is performed.

Conventionally, the removal of unnecessary organic substances has often been performed by a wet treatment using a chemical solution. However, in recent years when the wiring has become finer, the gaps between the mask patterns 104 and the inner diameter of the via hole 204 illustrated above have also become narrower, and the chemical solution is allowed to permeate into such a narrow space (and thus, the said. Removing unnecessary organic matter in space) is becoming more difficult.

Therefore, a method for removing unnecessary organic substances by a dry treatment instead of a wet treatment is being sought. For example, Patent Document 1 describes that desmear treatment is performed using oxygen plasma. Since plasma can enter a narrow space, smear in such a space can be reliably removed.

International Publication WO 2012/042846

In the technique of Patent Document 1, oxygen plasma is used for desmear treatment. Oxygen plasma is excellent in that it has a strong effect of removing organic substances, but when a substance that is easily oxidized is exposed on the surface of the object, treating this with oxygen plasma causes the substance to be oxidized. There is. For example, in each case shown in FIG. 1, the electrode is exposed on the surface of the object, and the material often used as the electrode is copper, which is a substance that is highly easily oxidized. Therefore, when an attempt is made to remove an organic substance using oxygen plasma in such a case, the copper electrode is oxidized to become a copper oxide.

Further, an object having a copper electrode exposed on the surface can be easily provided with a copper electrode on the surface without being treated by oxygen plasma, for example, by applying heat to the object or by simply creating an atmosphere containing oxygen. It is oxidized (thermal oxidation or natural oxidation).

If the surface of the copper electrode is oxidized and remains as a copper oxide, it causes poor connection (poor continuity).

The problem to be solved by the present invention is, for example, that copper oxide is formed on the surface of the exposed portion when removing unnecessary organic substances and the like from the surface of an object in which copper is exposed on at least a part of the surface. It is to provide technology that can be avoided from being left unattended.

The present invention made to solve the above problems
A plasma treatment method for reducing copper oxide on the surface of an object whose surface is exposed to copper at least in part.
The arrangement process of arranging the object inside the plasma processing chamber and
A water plasma forming step of introducing water or a mixture containing water as a plasma raw material into the plasma processing chamber and converting the plasma raw material into plasma.
Have.

The term "water" as used herein includes gaseous water (water vapor), liquid (water droplet) water, and solid (ice fog) water.
The composition of the "mixture containing water" other than water includes oxygen, air, nitrogen, argon, helium, hydrogen, nitrous oxide, and the like (details will be described later).

Water plasma (water plasma alone or mixed plasma containing at least a part of water plasma) is formed by using water or a mixture containing water as a plasma raw material and converting it into plasma. The present inventors have obtained through experiments that water plasma has a high reducing power (for example, FIGS. 6 to 8). Therefore, according to the water plasma, the copper oxide exposed on the surface of the object can be reduced back to copper. Further, since water plasma has a high organic substance removing action (for example, FIG. 14), if organic substances such as resist, scum, and smear remain on the surface of the object, they can be removed.

The reason is presumed as follows.
When the type and amount of substances existing in the plasma processing chamber where a single water plasma exists are measured using an analyzer, hydroxyl radicals, atomic hydrogen, and atomic hydrogen are found in the plasma processing chamber where the water plasma is formed. It was confirmed that atomic oxygen was present (Fig. 2). From this, it is presumed that the following chemical reactions (1) and (2) proceed in the plasma processing chamber where the water plasma is formed.
(1) Chemical reaction in which atomic oxygen and hydroxyl radical combine with organic substances attached to the object. Organic substances are removed from the object by this chemical reaction. That is, atomic oxygen and hydroxyl radicals in the plasma treatment chamber contribute to the removal of organic substances and the like.
(2) Chemical reaction (reduction) in which atomic hydrogen and copper oxide are bonded
Cu ₂ O + 2H → _{2 Cu + H 2} O
_{CuO + 2H → Cu + H 2} O
This chemical reaction reduces the copper oxide present on the surface of the object and returns it to copper. That is, the atomic hydrogen in the plasma processing chamber contributes to the reduction of the copper oxide.

The plasma treatment method according to the present invention is preferably
An oxygen plasma forming step of introducing oxygen gas into the plasma processing chamber and converting it into plasma after the arrangement step and before the water plasma forming step.
Further have.

Oxygen plasma has a stronger effect of removing organic substances than water plasma. Therefore, by forming an oxygen plasma before the water plasma and causing it to act on the object, the organic matter on the object can be sufficiently removed. Further, even if the copper on the surface of the object is oxidized by the oxygen plasma, it can be reduced by the water plasma and returned to the copper.

In the plasma treatment method according to the present invention, preferably
The mixture is a mixture of water vapor and oxygen, and the volume ratio of water vapor in the mixture is 50% or more.

In a mixture of water vapor and oxygen (mixed gas), the present inventors act on an object in which copper oxide is exposed on the surface by applying a plasma gas obtained by converting the mixed gas into plasma while changing the mixing ratio. I conducted an experiment to make it. As a result, it was confirmed that when the volume ratio of water vapor was 50% or more, the copper oxide was sufficiently reduced by the reducing power of water plasma (FIGS. 6 and 7). Therefore, by using such a mixed gas, the copper oxide on the surface of the object can be reduced back to copper.

As described above, the "mixture" which is the plasma raw material in the present invention may be a mixed gas of water vapor and a gas other than oxygen. The "gas other than oxygen" is, for example, _{a mixed gas of air, nitrogen (N 2} ), argon (Ar), helium (He), hydrogen (H ₂ ) and nitrogen, and the volume ratio of hydrogen is 4%. things, those volume ratio of hydrogen of 2.5% a mixed gas of hydrogen and argon, may be mentioned nitrous oxide (N 2 _O) and the like. As described above, the reaction for reducing copper oxide depends on the presence of atomic hydrogen derived from water plasma, and the higher the volume ratio of water vapor in the mixed gas, the more the reduction reaction is promoted. .. Therefore, if the oxidizing power of the gas mixed with water vapor in the mixed gas is smaller than oxygen, the volume ratio of water vapor may be smaller than 50%, and if the oxidizing power of the gas is larger than oxygen, the volume ratio of water vapor may be smaller. Is preferably greater than 50%.

In the plasma treatment method according to the present invention, preferably.
The mixture is a mixture of water vapor and oxygen, and the volume ratio of water vapor in the mixture is 50% to 70%.

The inventors conducted an experiment in which an organic substance on an object was removed from a mixture of water vapor and oxygen with a plasma gas obtained by converting the mixed gas into plasma while changing the mixing ratio. As a result, it was found that the effect of removing organic substances was particularly high in the mixed gas having a volume ratio of water vapor of 20% to 70% (Fig. 16). Therefore, if the volume ratio of water vapor in the mixed gas is 50 to 70%, both a high reducing action and a high organic matter removing action can be realized.

In the plasma treatment method according to the present invention, preferably
During the water plasma forming step, the pressure in the plasma processing chamber is maintained at 30 Pa or less.

The present inventors conducted an experiment in which water plasma was applied to an object whose surface was exposed to copper oxide while changing the pressure in the plasma processing chamber. We also conducted an experiment to remove organic substances on the object with water plasma while changing the pressure in the plasma processing chamber. From these experiments, it was found that the lower the pressure in the plasma processing chamber (for example, 30 Pa or less), the more the reducing action of water plasma and the removing action of organic matter tend to be sufficiently exerted (Fig. 12, FIG. 17). Therefore, if the plasma processing chamber is controlled to such a pressure, the reduction of the copper oxide can be promoted and the organic matter can be quickly removed.

Considering the above-mentioned organic matter removing action, the present invention is another aspect of the present invention.
A plasma treatment method for removing organic substances on an object.
The arrangement process of arranging the object inside the plasma processing chamber and
A water plasma forming step of introducing water or a mixture containing water as a plasma raw material into the plasma processing chamber and converting the plasma raw material into plasma.
Can be carried out as having.

Water plasma (water plasma alone or mixed plasma containing at least a part of water plasma) has a high reducing power. Therefore, by applying water plasma, the copper oxide on the surface of the object can be reduced to expose the copper, and it is possible to prevent the copper oxide from being left formed on the object. .. Water plasma also has a high organic matter removing action. Therefore, by allowing water plasma to act, organic substances such as resist, scum, and smear can be sufficiently removed.

The figure for demonstrating the scene which needs the process of removing the unnecessary organic matter existing on the surface. Data obtained by measuring the type and amount of substances present in a plasma processing chamber in which a single water plasma exists, using an analyzer. Schematic diagram of the plasma processing apparatus. The figure which shows the flow of plasma processing. Photographs of the copper plate and copper oxide plate used in the experiment. A table summarizing the treatment conditions and results related to the experiment for evaluating the reducing power of water plasma. A table summarizing the treatment conditions and results related to the experiment for evaluating the reducing power of water plasma. A table summarizing the treatment conditions and results related to the experiment for evaluating the reducing power of water plasma. Photograph of the appearance of the copper oxide plate after the experiment. Photograph of the appearance of the copper oxide plate after the experiment. Analysis results obtained by analyzing the depth direction of the sample by scanning X-ray photoelectron spectroscopy. The figure which shows the relationship between the process pressure and the reduction rate obtained by an experiment. A table summarizing the treatment conditions and results related to the comparative experiment for evaluating the organic matter removing action of water plasma. A table summarizing the treatment conditions and results related to the experiment for evaluating the organic matter removing action of water plasma. A graph summarizing the photoresist removal rate obtained by the experiment. The figure which showed the relationship between the volume ratio of oxygen in the mixture of water vapor and oxygen and the removal rate of a photoresist which was obtained by an experiment. The figure which shows the relationship between the process pressure obtained by an experiment, and the removal rate of a photoresist.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

<1. Device configuration>
The plasma processing apparatus according to the embodiment will be described with reference to FIG. FIG. 3 shows a schematic configuration of the plasma processing apparatus 100. As is clear from this figure, the plasma processing apparatus 100 is a parallel plate type (capacitively coupled) plasma processing apparatus.

The plasma processing apparatus 100 includes a plasma processing chamber 1 that internally forms a processing space V in which an object 9 is arranged, and water that introduces water (specifically, water vapor that is gaseous water) into the processing space V. An introduction unit 2, an oxygen gas introduction unit 3 that introduces oxygen gas into the processing space V, an exhaust unit 4 that exhausts the processing space V, a pair of electrodes 5 and 6 arranged to face the processing space V, and each of these parts. A control unit 7 for controlling the above is mainly provided.

The plasma processing chamber 1 is provided with a gas introduction port 11 for introducing gas into the processing space V and an exhaust port 12 for exhausting the inside of the processing space V. Pipes 22 and 32, which will be described later, are connected to the gas introduction port 11. Further, a pipe 42, which will be described later, is connected to the exhaust port 12.

The water introduction unit 2 includes a pipe 22 having one end connected to the gas introduction port 11 and the other end connected to the water supply source 21. In the middle of the pipe 22, a valve 23, a mass flow controller 24 that automatically adjusts the flow rate of the gas flowing through the pipe 22, and a vaporizer (vaporizing water to be steam) that vaporizes the introduced fluid (here, vaporizes water). The device) 25 is provided. Each of these units 23, 24, and 25 is electrically connected to the control unit 7, and the control unit 7 controls the introduction and stop of water vapor into the processing space V.

The oxygen gas introduction unit 3 includes a pipe 32 having one end connected to the gas introduction port 11 and the other end connected to the oxygen gas supply source 31. A valve 33 and a mass flow controller 34 that automatically adjusts the flow rate of gas flowing through the pipe 32 are provided in the middle of the pipe 32. Each of these units 33 and 34 is electrically connected to the control unit 7, and the control unit 7 controls the introduction and stop of oxygen gas into the processing space V.

The exhaust unit 4 includes a pipe 42 having one end connected to the exhaust port 12 and the other end connected to the exhaust line. A valve 43 and a vacuum pump 44 are provided in the middle of the pipe 42. Each of these units 43 and 44 is electrically connected to the control unit 7, and the control unit 7 controls the exhaust of gas from the processing space V.

Of the pair of electrodes 5 and 6 arranged to face each other in the plasma processing chamber 1, power is supplied to one of the electrodes 5 via an RF power supply 51 and a capacitor 52 (hereinafter, this electrode 5 is referred to as a "powered electrode". 5 "). The other electrode 6 is grounded (hereinafter, this electrode 6 is referred to as a "ground electrode 6"). In this configuration, by supplying RF power to the powered electrode 5, the gas introduced in the processing space V is turned into plasma. In the plasma processing apparatus 100, the object 9 to be processed is placed on the powered electrode 5 in a RIE (Reactive Ion Etching) mode and on the ground electrode 6 in a PE (Plasma Etching) mode. Plasma processing can be performed by selecting from modes, but either mode may be used in carrying out the present invention. In the example of the figure, for example, the case of plasma processing in the PE mode is illustrated.

The control unit 7 controls each of the above elements to execute a series of processes. The control unit 7 uses a personal computer as a hardware resource, and by executing dedicated control / processing software installed in the personal computer, various functional blocks required for the control are embodied. be able to.

<2. Process flow>
The plasma processing method according to the embodiment will be described with reference to FIG. FIG. 4 is a diagram showing a series of flows related to the processing method. The series of processes described below is performed by the plasma processing apparatus 100 described above.

The following treatment is a treatment for removing unnecessary organic substances and the like on the object 9 (particularly, the object 9 in which copper is exposed on at least a part of the surface), and specifically, for example, a copper electrode. Descam treatment of the substrate 101 on which the 102 was formed (FIG. 1 (a)), desmear treatment of the substrate 201 on which the copper electrode 202 was formed (FIG. 1 (b)), and a comb-shaped copper electrode 303 on the substrate 301. A treatment for removing the photoresist residue after the formation (FIG. 1 (c)) and the like are assumed.
However, the following treatment can also target the object 9 whose surface is not exposed to copper. For example, it can be applied as a treatment for removing the photoresist layer of an object 9 whose surface is covered with a photoresist layer.

First, the object 9 is arranged inside the plasma processing chamber 1 (step S1). Specifically, the object 9 is carried into the plasma processing chamber 1 through a carry-in port (not shown) and placed on, for example, the ground electrode 6 (or may be on the powered electrode 5). Then, the object 9 is fixed to this with an electrostatic chuck or the like.

Subsequently, an oxygen plasma is formed in the processing space V, and the object 9 is processed by this (step S2). Specifically, after closing the carry-in inlet and sealing the plasma processing chamber 1, oxygen gas is introduced into the processing space V, and at the same time, the processing space V by the vacuum pump 44 connected to the exhaust port 12 is used. Is exhausted to maintain the processing space V at a predetermined pressure. Subsequently, high frequency power is applied to the powered electrode 5. As a result, the oxygen gas introduced into the processing space V is turned into plasma, and oxygen plasma is generated on the upper part of the object 9.

Oxygen plasma has an action of removing organic substances. Therefore, by acting the oxygen plasma on the object 9, the organic matter on the object 9 is removed. On the other hand, at this time, the copper on the surface of the object 9 is oxidized by the oxygen plasma to form a copper oxide.

When the treatment with oxygen plasma is performed for a predetermined time, water plasma is subsequently formed in the treatment space V, and the object 9 is treated with this (step S3). Specifically, water vapor (or water vapor and oxygen gas) is introduced into the processing space V, and at the same time, the processing space V is exhausted by the vacuum pump 44 connected to the exhaust port 12, and the processing space is exhausted. V is maintained at a predetermined pressure (eg, 30 Pa or less). However, when introducing oxygen gas, the mixing ratio of oxygen gas and water vapor (specifically) so that the volume ratio of water vapor in the mixed gas (mixed gas of water vapor and oxygen) in the processing space V is 50% or more. It is preferable to adjust the introduction flow rate of each gas). Subsequently, high frequency power is applied to the powered electrode 5. As a result, the water vapor introduced into the processing space V (when oxygen gas is introduced, a mixed gas of water vapor and oxygen gas) is turned into plasma, and water plasma (mixed gas is generated above the object 9). When it is converted to plasma, a mixed plasma of water plasma and oxygen plasma) is generated. As a result, the water plasma treatment on the object 9 proceeds.

FIG. 2 shows data obtained by measuring the types and amounts of substances existing in the processing space V in the presence of a single water plasma with an optical emission spectrometer (Optical Emission Spectrometer). As shown here, the processing space V in the presence of water plasma contains a relatively large amount of hydroxyl radicals, a relatively large amount of atomic hydrogen, and a relatively small amount of atomic oxygen. There is. When a plasma of a mixed gas of water vapor and oxygen gas is formed in the processing space V, it is considered that the amount of atomic oxygen is further increased. As described above, the atomic oxygen and hydroxyl radicals existing in the processing space V remove the organic substances and the like adhering to the object 9 (organic substances and the like not removed in step S2). Further, the atomic hydrogen existing in the processing space V reduces the copper oxide existing on the object 9. That is, by acting the water plasma on the object 9, the organic matter on the object 9 is further removed, and the copper oxide existing on the surface of the object 9 is returned to copper.

When the treatment with water plasma is performed for a predetermined time, the treatment is terminated. Specifically, the valves 23 and 33 are closed to stop the supply of steam and oxygen gas, and the supply of high-frequency power is stopped. Subsequently, the processing space V is returned to atmospheric pressure, and the object 9 is carried out from the plasma processing chamber 1 (step S4).

In the above series of treatments, water vapor was introduced into the treatment space V when forming the water plasma in step S3, but liquid (water droplets) water, solid (ice fog) water, or These mixtures may be introduced into the processing space V.

Further, in the above series of treatments, in forming the water plasma in step S3, a substance other than oxygen may be introduced into the treatment space V in addition to water (or in addition to water and oxygen). Specifically, for example, a mixed gas of air, nitrogen, argon, helium, hydrogen and nitrogen having a volume ratio of hydrogen of 4%, and a mixed gas of hydrogen and argon having a volume ratio of hydrogen of 2.5%. , Dinitrogen monoxide, etc. may be introduced.

Further, in the above series of processes, the process of step S2 is not essential.

<3. Experiment on the action of water plasma>
<3-1. Experiment to evaluate the reducing power of water plasma>
In order to evaluate the reducing power of water plasma, a sample in which copper oxide was present on at least a part of the surface was prepared, and an experiment was conducted in which this was treated with water plasma. Specific experimental conditions are shown below.

As a sample, an oxidized copper plate (copper oxide plate) was placed on a glass plate (thickness 6 mm, 26 × 76 mm). Specifically, this copper oxide plate is obtained by heating a copper plate (CU-110607 manufactured by Niraco Co., Ltd., thickness 0.1 mm, 3 × 30 mm, purity 99.9%) with a hot plate to oxidize (thermally oxidize) the surface. Here, the copper plate was heated at 150 ° C. for 5 minutes (first copper oxide plate), the copper plate was heated at 180 ° C. for 5 minutes (second copper oxide plate), and the copper plate was heated at 200 ° C. for 30 minutes. Three types of copper oxide plates (third copper oxide plates) were prepared (Fig. 5). When the second copper oxide plate was measured with a reflection spectroscopic film thickness meter (FE-3000 manufactured by Otsuka Electronics Co., Ltd.), the thickness of the oxide film was about 26 nm. Moreover, when the third copper oxide plate was measured by this reflection spectroscopic film thickness meter, the thickness of the oxide film was about 70 nm.

The copper electrode is formed on the insulator in the actual processing steps such as death come true and death come true. Therefore, in order to form an environment close to this, a copper oxide plate is placed on the glass plate in this experiment. Another aim is to electrically insulate the copper oxide plate by placing it on the glass plate and eliminate the copper oxide removing action due to the above-mentioned sputtering effect.

The plasma processing apparatus that performs plasma processing on the sample has the same configuration as the plasma processing apparatus 100 described above, and specifically, a PC-300 manufactured by SAMCO Corporation was used. Further, using VC-1420 manufactured by Horiba STEC, Inc. as the vaporizer 25, nitrogen gas is sent to a glass container containing water, which is a water supply source 21, and water is introduced from the glass container into the vaporizer 25 to introduce the vaporizer. The water vapor vaporized in 25 is introduced into the processing space V via the mass flow controller 24. Further, the sample was placed on the ground electrode 6 of the plasma processing apparatus 100. As described above, the sample may be placed on the powered electrode 5, but in this case, the potential difference between the plasma and the sample becomes large, so that the ions are present in the sample due to the sputtering effect caused by the incident on the sample. Copper oxide may be removed. Therefore, in order to eliminate the copper oxide removing action due to such a sputtering effect and evaluate only the copper oxide removing action by water plasma, the sample was placed on the ground electrode 6.

The sample was treated under the treatment conditions shown in FIGS. 6 to 8, and the change in color before and after the treatment was observed. In Experiments 1 to 7 (Fig. 6), a second copper oxide plate (a copper oxide plate heated at 180 ° C. for 5 minutes) was placed on a glass plate as a sample, and this was used as a sample for each treatment condition in which the volume ratio of water vapor and oxygen was different. Processed with. In Experiments 8 to 10 (FIG. 7), the samples were processed under the same processing conditions as in Experiments 4 to 6, except that the processing time was changed (3 minutes → 15 minutes). In Experiments 11 to 17 (FIG. 8), a sample in which a third copper oxide plate (a copper oxide plate obtained by heating a copper plate at 200 ° C. for 30 minutes) was placed on a glass plate was used as a sample, and this was used under the same treatment conditions as in Experiments 1 to 7. Processed. However, in FIGS. 6 to 8, "no discoloration" means the color of the copper plate before oxidation.

FIG. 9 shows photographs of the appearance of the copper plate before thermal oxidation, the copper oxide plate after Experiment 7 (treated with a single oxygen plasma), and the copper oxide plate after Experiment 1 (treated with a single water plasma). There is. The copper oxide plate treated with a simple oxygen plasma had a blackish gray or purple color, and it was confirmed that the copper oxide was present. On the other hand, the copper oxide plate treated with a single water plasma returned to copper color, and it was confirmed that the copper oxide was reduced and returned to copper. In particular, the copper oxide plate treated with a single water plasma had a copper color with less dullness than the copper plate before thermal oxidation. It is considered that this is because the natural oxide film existing on the copper plate before thermal oxidation was reduced and disappeared. Thus, from Experiment 1, it was found that a single water plasma has a reducing power to reduce copper oxide.

FIG. 10 shows photographs of the appearance of the copper oxide plates after Experiments 1 to 10. Here, during the treatment, the lower half of the copper oxide plate is covered with a silicon wafer piece (5 mm × 10 mm) so that the change in color before and after the treatment can be easily compared. In Experiments 1 to 3 and 8, it was confirmed that the treated copper oxide plate returned to copper color. In other words, when processing a sample by converting a mixed gas of water vapor and oxygen into plasma, if the processing time is 3 minutes, the copper oxide is reduced when the volume ratio of water vapor is 60% or more, and the processing time is 15 minutes. For example, it was found that the copper oxide was reduced when the volume ratio of water vapor was 50% or more.

Further, from the comparison between Experiments 1 to 7 and Experiments 8 to 10, it was also found that if the treatment time is long, copper oxide is reduced even if the volume ratio of water vapor is small. However, if the processing time becomes excessively long, the plasma processing chamber 1 and the electrodes 5 and 6 arranged inside the plasma processing chamber 1 are heated, and this heat may oxidize (thermally oxidize) copper. Also, from the viewpoint of cycle time, it is not preferable that the processing time becomes excessively long. Under these circumstances, it is realistic to keep the treatment time to about 15 minutes or less, and considering this, it is sufficient that the volume ratio of water vapor is 50% or more in order to reduce the copper oxide. We can conclude.

Further, as described above, the oxide film thickness of the third copper oxide plate used in Experiments 11 to 17 is about 70 nm, and according to Experiments 11 to 17, all the copper oxides are reduced in a treatment time of 3 minutes. Therefore, it was found that the reduction rate of the copper oxide under the treatment conditions was about 23 nm / min or more.

In addition to the above experiments, the following experiments were also performed.
The following three types of samples A, B, and C were analyzed in the depth direction by Ar beam sputtering etching of a scanning X-ray photoelectron spectroscopy analyzer: ESCA (PHI 5000 VersaProbe II manufactured by ULVAC PHI Co., Ltd.). FIG. 11 shows the analysis result. In the graph shown here, the horizontal axis represents the Ar beam sputtering time, and the vertical axis represents the composition ratio (Atomic Concentration (%)). Further, in the graph, Cu2p 3/2 shows an electron derived from a copper atom, O1s shows an electron derived from an oxygen atom, and C1s shows an electron derived from a carbon atom.
Sample A: Third copper oxide plate (copper oxide plate heated at 200 ° C. for 30 minutes)
Sample B: Copper plate treated under the treatment conditions of Experiment 7 (treated with oxygen plasma) Sample C: Sample B treated under the treatment conditions of Experiment 1 (treated with water plasma)

In sample A, it took about 8 minutes for O1s to disappear. In sample B, it took about 7 minutes for O1s to disappear. On the other hand, in sample C, O1s disappeared in 0.5 minutes. As described above, the oxide film thickness of the third copper oxide plate of sample A is about 70 nm. Therefore, considering this and the time required for the disappearance of O1s, the copper oxide film present in sample B is present. The thickness is about 61 nm (70 nm × 7 min / 8 min), and the film thickness of the copper oxide present in sample C can be estimated to be about 4 nm (70 nm × 0.5 min / 8 min). In other words, it can be seen that the thickness of the copper oxide, which was about 61 nm, was reduced to about 4 nm by the water plasma. The 4 nm film thickness is thinner than the natural oxidation film thickness. In this way, analysis experiments in the depth direction of samples A, B, and C confirm that the copper oxide was reduced by water plasma and almost completely disappeared (that is, water plasma has reducing power). Was done.

In addition to the above experiments, the following experiments were also performed.
A sample of a second copper oxide plate (copper oxide plate heated at 180 ° C for 5 minutes) placed on a glass plate is treated with a single water plasma, and it takes time for the copper oxide to be reduced and disappear. (Specifically, the time required for the copper oxide plate to return to the copper color) was measured. This experiment was carried out under each treatment condition with different steam flow rates (however, the process pressure also changed according to the steam flow rate. In all other treatment conditions, the RF power was 250 W and the treatment time was 3 minutes. Common).

As a result, the time required for the copper oxide to be reduced and disappeared was 20 seconds when the water vapor flow rate was 5 sccm (process pressure 5 Pa), and when the water vapor flow rate was 10 sccm (process pressure 9 Pa). It was 25 seconds, and when the steam flow rate was 50 sccm (process pressure was 20 Pa), it was 45 seconds.
As described above, since the oxide film thickness of the second copper oxide plate used in this experiment is about 26 nm, the reduction rate of the copper oxide under each treatment condition should be calculated from this and the time obtained in the above experiment. Can be done. The relationship between the process pressure and the reduction rate thus obtained is shown in FIG. As can be seen from this figure, experiments have shown that the lower the process pressure, the faster the reduction rate. Therefore, it can be concluded that a low process pressure (for example, 30 Pa or less) is preferable for effective reduction of copper oxide.

<3-2. Experiments to evaluate the removal effect of organic matter in water plasma>
In order to evaluate the strength of the organic matter removing action of water plasma, a sample in which an organic matter layer (specifically, a photoresist layer) was formed on the surface was prepared, and an experiment was conducted in which this was treated with water plasma. Specific experimental conditions are shown below.

A photoresist with a thickness of 1.0 μm (THMR-IP3250 manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied on a silicon wafer, and this was further baked at 110 ° C for 5 minutes and placed on a glass plate. Was used as a sample. As the plasma processing apparatus 100 for performing plasma processing on the sample, the same one as in each of the above experiments was used.

The sample was treated under the treatment conditions shown in FIGS. 13 to 14, the change in the film pressure of the photoresist at that time was measured, and the removal rate of the photoresist (so-called ashing rate) was calculated from the measurement. An ellipsometer (ESM-1A manufactured by ULVAC, Inc.) was used to measure the film thickness of the photoresist. Experiments 18 to 22 are comparative experiments of Experiments 23 to 24, and here, a mixture of hydrogen and nitrogen (Experiment 18), nitrogen (Experiment 19), a mixture of hydrogen and argon (Experiment 20), and argon (Experiment 21). The samples were treated with plasma gas, which was converted into plasma. In Experiments 22 to 24, the sample was treated with plasma gas obtained by converting oxygen (Experiment 22), water vapor (Experiment 23), and a mixed gas thereof (Experiment 24) into plasma. The treatment conditions other than the type of plasma gas were common to each experiment 18 to 24.

FIG. 15 graphs the removal rates of photoresists obtained from each of Experiments 23 and 24 and Comparative Experiments 18-21. As shown here, when Experiment 23 (water vapor) and Experiment 24 (mixed gas of water vapor and oxygen) are compared with Comparative Experiments 18 to 21, water plasma (water plasma (mixed gas of water vapor and oxygen) is compared with the plasma of each gas used in the comparative experiment. It was found that water plasma alone or mixed plasma of oxygen plasma and water plasma) can remove the photoresist quickly enough.

Further, it has been conventionally known that oxygen plasma has a high photoresist removing effect, and such a result is shown in Experiment 22, but when Experiment 22 and Experiment 23 are compared, it is sufficient for water plasma alone. Was found to have a high photoresist removing effect.
Furthermore, when Experiment 22 and Experiment 24 were compared, it was found that the mixed plasma of oxygen plasma and water plasma had a higher photoresist removing effect than the oxygen plasma alone. In FIG. 16, the photoresist removal rate in each case of treatment under the same treatment conditions as in Experiments 22 to 24 except that the mixing ratio of water and oxygen was changed is plotted on the graph. As shown here, in a mixture of water vapor and oxygen, the photoresist removal rate is in the range of 30% to 80% volume ratio of oxygen (range of 20% to 70% volume ratio of water vapor). It was found that it was particularly enhanced (that is, the photoresist removing effect was particularly enhanced). As described above, in order to reduce the copper oxide, it is known that the volume ratio of water vapor should be 50% or more. Therefore, if the volume ratio of water vapor is 50 to 70%, a high reducing action is obtained. It can be said that both high organic matter removing action can be realized.

In addition to the above experiments, the following experiments were also performed.
Using the same sample as in Experiments 18 to 24, the change in the film pressure of the photoresist when this was treated with a single water plasma was measured using the above ellipsometer, and the removal rate of the photoresist was calculated from the measurement. This experiment was carried out under each treatment condition with different steam flow rates (however, the process pressure also changed according to the steam flow rate. In all other treatment conditions, the RF power was 250 W and the treatment time was 3 minutes. Common).

As a result, the photoresist removal rate (ashing rate) is 42.2 (nm / min) when the water vapor flow rate is 5 sccm (process pressure is 5 Pa), and 34.9 when the water vapor flow rate is 10 sccm (process pressure is 9 Pa). It was (nm / min) and was 18.8 (nm / min) when the water vapor flow rate was 50 sccm (process pressure was 20 Pa). The relationship between the process pressure thus obtained and the photoresist removal rate is shown in FIG. As can be seen from this figure, experiments have shown that the lower the process pressure, the faster the photoresist removal rate. Therefore, it can be concluded that a low process pressure (eg, 30 Pa or less) is preferable for effective photoresist removal.

100 ... Plasma treatment device 1 ... Plasma treatment room 11 ... Gas inlet 12 ... Exhaust port 2 ... Water inlet 21 ... Water supply source 22 ... Piping 23 ... Valve 24 ... Mass flow controller 25 ... Vaporizer 3 ... Oxygen gas inlet 31 ... Oxygen gas supply source 32 ... Piping 33 ... Valve 34 ... Mass flow controller 4 ... Exhaust section 42 ... Piping 43 ... Valve 44 ... Vacuum pump 5 ... Powered electrode 51 ... RF power supply 52 ... Condenser 6 ... Ground electrode 7 ... Control section 9 ... Target Object 101 ... Substrate 102 ... Electrode 102 ... Copper electrode 103 ... Photoresist layer 104 ... Mask pattern 104a ... Hemming portion 104b ... Eave-shaped portion 201 ... Substrate 202 ... Electrode 202 ... Copper electrode 204 ... Via hole 204a ... Smear 301 ... Substrate 302 ... Photoresist pattern 302a ... Development residue 303 ... Copper electrode

Claims (2)

A plasma treatment method for reducing copper oxide on the surface of an object whose surface is exposed to copper at least in part.
The arrangement process of arranging the object inside the plasma processing chamber and
A water plasma forming step of introducing a mixture containing water into the plasma processing chamber as a plasma raw material and converting the plasma raw material into plasma.
Have,
A plasma treatment method in which the mixture is a mixture of water vapor and oxygen, and the volume ratio of water vapor in the mixture is 50% or more. The plasma processing method according to claim 1.
An oxygen plasma forming step of introducing oxygen gas into the plasma processing chamber and converting it into plasma after the arrangement step and before the water plasma forming step.
A plasma processing method further comprising.